Digital Versus Film Mammography

Digital versus Film Mammography for Breast Cancer Screening

What is the problem and what is known about it so far?
Breast cancer screening has been shown to decrease death rates and is the most well studied form of cancer screening. The goal of screening for breast cancer is to find disease at an early stage before a patient has symptoms, and at a point where the disease may be curable. The US Preventive Task Force currently recommends that all women undergo screening mammography starting at the age of 40 and continuing screening every one to two years there after. Those with a family history of breast cancer may need more frequent screening, and to start at a younger age. Studies have shown that finding cancer using mammography is more difficult in younger women, largely due to the very dense and fibrous breast tissue commonly seen in these women. Other factors such as the use of hormone replacement therapy, menopause and body weight can affect the accuracy of mammography.

Why did the researchers do this particular study?
Digital mammography was developed as a way of obtaining better pictures of the breast in order to find hidden cancers. Digital mammography replaces x-ray film with special detectors that convert x-rays into electric signals, similar to those found in digital cameras. This study was designed to compare standard film mammography to digital mammography in the ability to detect breast cancer.

Who was studied?
42,760 women at 33 different hospitals in the US and Canada were studied. These women had no history of breast cancer and did not have any symptoms. Women of all different ages, races, and breast types were included in the study. Those with breast implants and women who were pregnant were not included.

How was the study done?
All women underwent both film mammography and digital mammography, and two different radiologists reviewed these studies. The radiologist looked at the density of the breast tissue and looked for any signs of cancer. If the radiologist found any signs of cancer on either type of mammography, further tests for breast cancer were undertaken. If no signs of cancer were present the women were asked to return in 1 year for another mammogram. The women in the study were followed 15 months and a total of 335 breast cancers were identified. Researches then used this information to compare digital mammography and film mammography.

What did the researchers find?
This study demonstrated that for women under the age of 50 years, those who have dense breasts and those who are pre-menopausal, digital mammography is better than film mammography at detecting early signs of cancer. However, for women over 50 and those who have stopped having menstrual periods, plain film mammography and digital mammography have equal accuracy. It is also important to note that neither method can detect all breast cancers, which stresses the importance of regular breast exams by a physician.

What were the limitations of the study?
This study did not attempt to prove that digital mammography could save lives. It is assumed that by finding cancers that would have otherwise been missed in younger women, lives can be saved. However, it is important to remember that this is a belief and further studies will be needed to look at the long-term impact of this type of screening. Another limitation of this study is that it did not address the increased cost of digital mammography. This type of screen may cost as much as 4 times more than film mammography. A follow up cost analysis study will address this issue.

What are the implications of the study?
For women over the age of 50 years, film mammography is less costly and just as accurate as the newer digital mammography. However, for women under the age of 50, those who are still having menstrual periods and those who have very dense breasts, digital mammography is more accurate. Because of this, newer digital mammography may have a very real role in the screening of younger women and may provide a better option for women with dense breast tissue.

Summarized by Jenna Williams, College of Medicine, University of Vermont
Summarized from "Diagnostic Performance of Digital versus Film Mammography for Breast-Cancer Screening." Pisano E. et al., New England Journal of Medicine, October 27, 2005, Volume 353, Number 17, pages 1773-1783.